Mine runs a lot cooler now. I still see coolant spike up to around 100ish C when stopped in hot weather, but I think that's normal? I haven't tested it on a real hot day lately. I just swapped in new fans, not sure if they made a difference. I'm still not sure what the underlying issue was. It really seemed to get a lot better with the 2nd coolant flush and the dealership that did that said it still had a lot of the original coolant in it (they could tell by the color), so I guess the first coolant flush another dealership did wasn't done properly. They also added water wetter. I've heard some people say that the LP640 should pretty much never get above 90c coolant temperature but maybe they live in colder climates.
My voltage also seems to drop as my car gets hot (It will hit around 11.9v). The new alternator didn't make a difference. Not sure if the alternator is just getting heat soaked or if it could be ground related?
The alternator belt tightening is interesting. I wonder if as my car heats it could be losing some tension on the belt slightly and it possibly slipping some like yours?